Psalm 34:19-20

Many are the afflictions of the righteous, But the Lord delivers him out of them all. He guards all his bones; Not one of them is broken.

The Psalmist here anticipates the thought which often arises in the mind. 

How can it be that God has a care about the righteous, who are continually harassed with so many calamities and trials? 

What purpose does the protection of God serve, unless those who are peaceably inclined enjoy peace and repose? 

What is more unreasonable, than that those who cause trouble to no one should themselves be tormented and afflicted in all variety of ways?

That, therefore, the temptations by which we are continually assailed may not shake our belief in the providence of God, we ought to remember this lesson of instruction, that although God governs the righteous, and provides for their safety, they are yet subject and exposed to many miseries, that, being tested by such trials, they may give evidence of their invincible constancy, and experience so much the more that God is their deliverer. If they were exempted from every kind of trial, their faith would languish, they would cease to call upon God, and their piety would remain hidden and unknown. 

It is, therefore, necessary that they should be exercised with various trials, and especially for this end, that they may acknowledge that they have been wonderfully preserved by God amidst numberless deaths. If this should seldom happen, it might appear to be fortuitous, or the result of chance; but when innumerable and interminable evils come upon them in succession, the grace of God cannot be unknown, when he always stretches forth his hand to them.

David, therefore, admonishes the faithful never to lose their courage, whatever evils may threaten them; since God, who can as easily deliver them a thousand times as once from death, will never disappoint their expectation. What he adds concerning “their bones”, seems not a little to illustrate the truth of this doctrine, and to teach us that those who are protected by God shall be free from all danger. He therefore declares, that God will take care that not one of their bones shall be broken; in which sense Christ also says, that “the very hairs of our head are all numbered,” [ 1 ] 

Luke 12:7

Indeed, the very hairs of your head are all numbered. Do not fear; you are more valuable than many sparrows.

“Not one of his bones shall be broken” not only points to the protection of the righteous, but also prophetically points to the cross.

John 19:36

For these things came to pass to fulfill the Scripture, “Not a bone of Him shall be broken.”

Exodus 12:46

In one house it shall be eaten; you shall not carry any of the flesh outside the house, nor shall you break one of its bones.

Numbers 9:12

They shall leave none of it until morning, nor break one of its bones. According to all the ordinances of the Passover they shall keep it.

Zechariah 12:10

“And I will pour on the house of David and on the inhabitants of Jerusalem the Spirit of grace and supplication; then they will look on Me whom they pierced. Yes, they will mourn for Him as one mourns for his only son, and grieve for Him as one grieves for a firstborn.

John 19:31-37

Therefore, because it was the Preparation Day, that the bodies should not remain on the cross on the Sabbath (for that Sabbath was a high day), the Jews asked Pilate that their legs might be broken, and that they might be taken away. Then the soldiers came and broke the legs of the first and of the other who was crucified with Him. But when they came to Jesus and saw that He was already dead, they did not break His legs. But one of the soldiers pierced His side with a spear, and immediately blood and water came out. And he who has seen has testified, and his testimony is true; and he knows that he is telling the truth, so that you may believe. For these things were done that the Scripture should be fulfilled,“Not one of His bones shall be broken.” And again another Scripture says, “They shall look on Him whom they pierced.”

Cited Sources:  Commentary Volume 4 by John Calvin [ 1 ] ,